The present invention relates to an image rendering apparatus, a head up display, and an image luminance adjusting method and to, in particular, a laser scanning image rendering apparatus and a head up display and an image luminance adjusting method that use the laser scanning image rendering apparatus.
Image display apparatuses that use optical scanners including scanning mirrors and raster scan laser beams to thereby display images on projection surfaces are well known (e.g., Japanese Unexamined Patent Application Publication No. 2014-132286). That is, the laser scanning image display apparatus reciprocally rocks the scanning mirror in a vertical direction according to the number of scanning lines that constitute an image at the same time as it reciprocally rocks the scanning mirror to the right and left in order to render scanning lines in a horizontal direction.
The laser scanning image rendering apparatus can be applied to, for example, an on-vehicle head up display. Video is rendered on the on-vehicle head up display through a windshield or a combiner that is present in front of a driver. Then, beams emitted from a laser light source and external light transmitted through the windshield are overlaid (overlapped) and the overlaid beams and light reach the eyes of the driver. In this way, the driver can see scenery in front of the driver together with video information.
If the laser scanning image rendering apparatus is used for the on-vehicle head up display, when surroundings are bright during the daytime, images with high contrast can be rendered because a luminance of laser beams can be made high. On the other hand, when the surroundings are dark during the nighttime, it is desired to render images with a low luminance in order to improve the visibility of the images for the driver.